So, what exactly will Detroit’s next mayor do for a living?

Kevyn Orr

FORTUNE — Who on earth would want to lead Detroit, the once-roaring auto town that’s now $18 billion in debt?

Democrats Benny Napoleon, former chief of Detroit Police, and Mike Duggan, former executive at Detroit Medical Center, are both vying to be mayor of Detroit in a race to be decided by voters on Tuesday.

But whoever wins the job won’t actually be in charge. That responsibility belongs to Kevyn Orr, a Washington, D.C.-based lawyer who was appointed as emergency manager of the floundering city in March and has the power to make decisions in place of elected city officials.

In a city still unsure if it belongs in bankruptcy, add this layer to an already awkward state of flux.

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As of Monday, Duggan was leading in the polls. He’s touted his turnaround prowess, pointing to his rescue of the Detroit Medical Center, the Wayne County government, and the city’s suburban bus system. That experience, Duggan says, qualifies him to rebuild Detroit. Napoleon, citing his law enforcement background, has pinned his candidacy and the future of Detroit on reducing crime and says that Detroit will not recover until its residents feel safe.

Campaign promises are one thing; implementing them, of course, is another, especially in cash-strapped Detroit, where fixing a broken streetlight is a burden too great. To measure the success either candidate will have at executing his agenda, look no further than current Detroit Mayor Dave Bing, who announced he wouldn’t seek reelection in May and has been elbowed out of city decisions ever since Orr and his team of advisors came to town.

In finding a new police chief, for instance, Bing’s choice of an insider took a back seat to Orr’s pick, James Craig, the former Cincinnati chief of police. Craig now answers to Orr’s appointees, as does the fire chief and leaders of the city’s law, finance, building, transportation, and water and sewer departments.

Bing told the Detroit Free Press that, once in office, the next mayor will find a reality in which “they’re not going to have the final say on anything.”

Orr’s tenure as city emergency manager runs through next fall, when his contract renewal will be up for a mayor and city counsel vote. Until then, what’s become a one-sided power-struggle between him and the office of the mayor is an “odd situation that’s almost unprecedented,” says D. Scott DeRue, director of the Ross Leadership Initiative at University of Michigan’s business school.

In the absence of any formal power or ability to spend money without Orr’s approval, the new mayor’s only option for building influence is to do so from the ground up with his social capital and networks within the city, says DeRue. Duggan could do that through his health care and business connections. Napoleon could tap his law enforcement ties. The mayor can capitalize on that clout once he’s handed the city’s reins.

That’s a tough task, but the bigger challenge might come from what DeRue warns against: badmouthing the governor and emergency manager in the hopes of gaining credibility among constituents. “The mayor has to see himself as a partner with Orr,” he says. “Being an adversary would just continue the conflict that’s already present.”

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But both candidates have already caved to temptation to gain political points by saying that they want Orr ousted and his responsibilities designated to the mayor’s office.

That means it’s up to Orr, who oversees the mayor’s pay and power and isn’t going anywhere, to make an overture. Bing, by not seeking reelection, took himself out of the equation to determine Detroit’s future. But the new mayor will be a big factor.

Orr “can’t see the new mayor as a figurehead with no power,” DeRue says. If he does, he’s doing a disservice to the city he’s been asked to save.

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